Protein expression during heat stress in thermo-intolerant and thermo-tolerant diatoms

Diatoms (Chrysophyta) are photosynthetic microorganisms that are abundant in the natural environment and often associated with specific habitat and water quality conditions. Their significance as bioindicators and as exploitable sources of fine chemicals makes them desirable candidates for the study of stress responses. The protein expression of a thermo-intolerant (Phaeodactylum tricornutum) and thermo-tolerant (Chaetoceros muelleri) diatom following exposure to elevated temperature was investigated using one- and two-dimensional gel electrophoresis and Western blot analysis. It was determined using SDS PAGE with ³⁵S-methionine labeled proteins and Western blot analysis using pea HSP70 antisera that higher temperatures and longer duration treatment were required to cause a noticeable stress response in C. muelleri compared to P. tricornutum. This may be explained by C. muelleri possessing higher amounts of constitutively expressed heat shock proteins, which allows these cells to rapidly adjust to temperature increases. Two-dimensional gel electrophoresis revealed that putative small heat shock proteins (smHSPs) may appear to play a role during heat stress in both diatoms, which is similar to the response in plants. SDS PAGE data are also presented characterizing the recovery of P. tricornutum after heat shock. These results suggest that there is a lag period between heat shock and stress protein synthesis in these thermo-intolerant cells. This supports the hypothesis that cells without higher amounts of constitutively expressed stress proteins have a greater sensitivity to increased temperature. Work is underway to identify particular stress proteins responsible for conveying thermo-tolerance and to determine if overexpression of these genes in thermo-intolerant diatoms affects their temperature sensitivity.     

(n-7) and (n-9) cis-Monounsaturated fatty acid contents of 12 Brassica species

cis-Vaccenic acid or cis-11-octadecenoic acid, a C18:1 (n-7) isomer of oleic acid (C18:1 (n-9)) has been found in several oilseeds. It is synthesized from palmitic acid (C16:0) via production of C16:1 (n-7) by a Delta9 desaturase and elongation by an elongase giving C18:1 (n-7). In this study, the fatty acid composition of 12 Brassica species was analyzed by GC-FID and confirmed by GC-MS. All species contained C18:1 (n-7), C20:1 (n-7) and C22:1 (n-7) fatty acid isomers, suggesting that C18:1 (n-7) was elongated. The levels of these fatty acids varied according to the species. C18:1(n-7)) represented from 0.4% to 3.3% of the total relative fatty acid contents of the seeds. The contents of C20:1(n-7) and C22:1(n-7) levels were lower than C18:1(n-7) contents; the relative fatty acid composition varied from 0.02% to 1.3% and from below the limit of detection to 1.3% for C20:1 (n-7) and C22:1 (n-7), respectively. The ratios of (n-7)/(n-9) ranged from 2.8% to 16.7%, 0.6% to 29.5% and 0% to 2.6% for C18:1, C20:1 and C22:2, respectively. Using statistical similarities or differences of the C18:1 (n-7)/(n-9) ratios for chemotaxonomy, the surveyed species could be arranged into three groups. The first group would include Brassica napus, B. rapa, and B. tournefortii with Eruca sativa branching only related to B. napus. The second group would include B. tournefortii, Raphanus sativus and Sinapis alba. The last group would include B. juncea, B. carinata and B. nigra with no similarity/relationship between them and between the other species. Results suggested that the level of C20:1 (n-7) influenced the levels of all monounsaturated fatty acids with chain length higher than 20 carbons. On the other hand, palmitoleic acid (C16:1) levels, C16:1 being the parent of all (n-7) fatty acids, had no statistically significant correlation with the content of any of the fatty acids of the (n-7) or (n-9) family.     

Fatty acid composition of Ruditapes decussatus spat fed on different microalgae diets

The fatty acid composition of the Ruditapes decussatus spat fed on three different microalgal diets during 4 weeks was determined. The fatty acid pattern of each diet was also analysed. The diets used were Isochrysis galbana, clone T-ISO, Tetraselmis suecica, and Phaeodactylum tricornutum. The fatty acid composition of the spat was usually well correlated with that of the diet supplied. Major differences among spat cultures were found in 14:0, 16:0, 16:1n-9, 16:1n-7, 18:1n-9, 18:2n-6, 18:3n-3, 18:4n-3, 20:5n-3, 22:5n-6 and 22:6n-3 fatty acids. These differences were correlated with the particular fatty acid content of each diet supplied. It has been shown that R. decussatus spat have a very low capacity to elongate and desaturate linolenic acid to n-3 PUFA, so when 20:5n-3 or 22:6n-3 were not present in the diet, they were also absent, at least in measurable amounts, in the clams. The absence of any of the “essential” fatty acids, 20:5n-3 in T-ISO or 22:6n-3 in Tetraselmis, did not limit spat growth, so their role as “essential” fatty acids might be a matter for discussion. Finally, the nutritive value of each diet was discussed in terms of its fatty acid composition.     

Changes in fatty acid composition of Mytilus galloprovincialis (Lmk) fed on microalgal and wheat germ diets

Dietary fatty acid incorporation and changes in various lipid and phospholipid classes in the mussel Mytilus galloprovincialis subjected to three different dietary regimens were analysed and compared. Group A was unfed; group B received a diet consisting of 100% Thalassiosira weissflogii, exhibiting the typical fatty acid composition of diatoms, and group C received a diet consisting of 100% wheat germ conferring a 18:2:n-6 abundance. Biochemical analyses of diets and mussels were carried out at the beginning and at the end of the 30-day experimental period. Starvation and T. weissflogii based diet poorly affected mussel growth and fatty acid composition which remained unchanged. On the contrary, the wheat germ-based diet increased the condition index and deeply affected the fatty acid profile of all lipid and phospholipid classes. The high dietary 18:2n-6 level drastically reduced tissue content of 20:4n-6, 20:5n-3 and 22:6n-3. The biosynthesis of Non Methylene Interrupted (NMI) dienoic fatty acid appeared to be insensitive to the high input of 16:1n-7 and 18:1n-9 respectively from diet B and C, and to the PUFA shortage of diet C. Nevertheless the two NMI trienoic derivatives, 20:3Δ5,11,14 and 22:3Δ7,13 16, were found higher in C with respect to other groups, presumably due to the high 18:2n-6 content of this diet.     

Fatty acid composition of individual polar lipid classes from marine macrophytes

Major glycolipids [monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG)) and phospholipids (phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylglycerol (PG)] as well as betaine lipid 1,2-diacylglycero-O-4'-(N,N,N-tri-methyl)-homoserine (DGTS) were isolated from Anfeltia tobuchiensis (Rhodophyta), Laminaria japonica, Sargassum pallidum (Phaeophyta), Ulva fenestrata (Chlorophyta) and Zostera marina (Embriophyta), harvested in the Sea of Japan. GC analysis of their fatty acid (FA) composition revealed that the n-6 polyunsaturated FAs (PUFAs) shared the most part of the sum of n-6 and n-3 PUFAs in PC and PE compared with glycolipids and PG. In algae, it was related to the prevalence of 20:4n-6 over 20:5n-3 in non-photosynthetic lipids. Percentage of n-6 PUFAs as well as the sum of n-3 and n-6 PUFAs decreased in the following sequence: PC-->PE-->PG. The saturation increased in the lines of MGDG-->DGDG-->SQDG and PC-->PE-->PG. PG was close to SQDG by the level of saturation. Distribution of C(18) and C(20) PUFAs in polar lipids depended on taxonomic position of macrophytes. Balance between C(18) and C(20) PUFAs was preferably shifted to the side of C(20) PUFAs in PC and PE that was observed in contrast to glycolipids and PG from L. japonica containing both series of FAs. The set of major FAs of polar lipid classes can essentially differ from each other and from total lipids of macrophytes. For example, MGDG was found to accumulate characteristic fatty acids 16:4n-3, 16:3n-3, 18:3n-6 and 18:4n-3, 20:3n-6 in U. fenestrata, Z. marina, L. japonica and S. pallidum, respectively.     

Algicidal activity of polyunsaturated fatty acids derived from <Emphasis Type="Italic">Ulva fasciata</Emphasis> and <Emphasis Type="Italic">U. pertusa</Emphasis> (Ulvaceae,Chlorophyta) on phytoplankton

Isolation of algicidal compounds from Ulva fasciata revealed that the algicidal substances were the polyunsaturated fatty acids (PUFAs) as hexadeca-4,7,10,13-tetraenoic acid (HDTA) C16:4 n-3, octadeca-6,9,12,15-tetraenoic acid (ODTA) C18:4 n-3, α-linolenic acid (ALA) C18:3 n-3 and linoleic acid (LA) C18:2 n-6. The fatty acid composition of four species of Ulvaceae (U. fasciata, U. pertusa, U. arasakii and U. conglobota) was analyzed by capillary gas chromatography to investigate the relationship with the algicidal activity. The results indicate that highly algicidal species, U. fasciata and U. pertusa, showed higher contents of C16:4 n-3, C18:3 n-3, and C18:4 n-3. Concentrations of these PUFAs released from the seaweed in the culture medium were also analyzed. These PUFAs were found to be significantly active against Chattonella antiqua, C. marina, Fibrocapsa japonica, Heterosigma akashiwo, Karenia mikimotoi, moderately effective against Heterocapsa circularisquama, Prorocentrum minimum, P. sigmoides, Scrippsiella trochoidea, whereas low effective against Alexandrium catenella and Cochlodinium polykrikoides. It is suggested that the PUFAs are useful mitigation agents to remove several harmful effects without causing detrimental effects on surrounding marine living organisms.     

Effects of changes in ambient PAR and UV radiation on the nutritional quality of an Arctic diatom (Thalassiosira antarctica var. borealis)

Polyunsaturated fatty acids (PUFAs) are essential macromolecules that are synthesized by phytoplankton during spring bloom, and they play a key role in the Arctic food web. They are, however, considered to be sensitive to oxidation by UV radiation (280-400 nm). Changes in the food quality of primary producers may affect the transport of biomass and energy in the whole ecosystem. Using a common Arctic diatom, we looked at the effect of ambient and increased UV radiation on its nutritional quality, specifically, the fatty acid composition and elemental ratios. In May 2004, in the archipelago of Svalbard (79° N), a unialgal culture of Thalassiosira antarctica var. borealis was subjected to a 17-day experiment in outdoor aquaria. The diatoms were kept in semi-continuous culture (40 1) and exposed to three treatments with different levels of UV radiation: none (UV-shielded), ambient, and enhanced. Fatty acid composition, C:N:P ratios, photosynthetic pigment composition, optimum quantum yield of PSII, and cell numbers were analysed over the experimental period. An initial increase in PAR (photosynthetically active radiation, 400-700 nm) intensities profoundly affected the fatty acid composition and substantially inhibited the synthesis of PUFAs, but the relative amounts of PUFAs were not reduced by UV radiation. Enhanced UV radiation did, however, cause a significant reduction in optimum quantum yield of PSII and affected some fatty acids, mainly 18:0 and 16:1 n-7, during the first week of the experiment. Both ambient and enhanced UV radiation caused significantly lower C:P and N:P ratios. At the same time, these treatments elicited a higher relative content of the photoprotective pigments diadinoxanthin and diatoxanthin. After acclimation to the new light levels these effects faded off. Thus, brief periods with high light exposure may cause significant changes in photosynthetic activity and food quality, but the capacity for photo-acclimation seems high. The impact of UV radiation seems to be less important for food quality than that of PAR during a sudden rise in total light intensity.     

Assimilation and biosynthesis of lipids in Arctic Calanus species based on feeding experiments with a C labelled diatom

The dominant Arctic Ocean and North Atlantic copepods Calanus hyperboreus, Calanus glacialis, and Calanus finmarchicus were collected in the Greenland Sea and fed ¹³C labelled diatom Thalassiosira weissflogii to follow the transfer and assimilation of carbon, lipid, and individual fatty acids and alcohols. The diatom was grown with ¹³C for 3 to 5 days and fed then to the copepods. During the feeding period of 14 days, total carbon increased in the copepodite stages V of C. hyperboreus and C. finmarchicus, whereas carbon remained almost constant in C. glacialis females. However, total lipid increased in all species and stages. Highest lipid accumulation occurred in C. hyperboreus in which nearly all lipids were exchanged already after 11 days of feeding. In the other species lipid accumulation made up between 22% (C. finmarchicus) and 45% of total lipid (C. glacialis). The proportion of wax esters was high ranging from 76% of total lipid in C. glacialis to 92% in C. finmarchicus. The fatty acid composition of the alga was dominated by 16:1(n-7), 16:0, 20:5(n-3), and 22:6(n-3). The composition of the copepods was similar because of feeding already on diatoms in the field. In addition, the monounsaturated fatty acids and alcohols, 20:1(n-9) and 22:1(n-11), were major components of the copepod lipids. During the feeding period the highest ¹³C labelling was always found in the C₁₆ polyunsaturated fatty acids and in the 16:1(n-7) alcohol. Because these components occurred only in trace amounts in the copepods they totally originated from the diet explaining the high labelling. It is noteworthy that the 16:1(n-7) alcohol originated only from the corresponding dietary and not from the abundant internal fatty acid. The long-chain monounsaturated fatty acids and alcohols, 20:1(n-9) and 22:1(n-11), are not existent in phytoplankton and have to be produced de novo. They were less labelled in the smaller species but highly ¹³C enriched in C. hyperboreus. Although dietary fatty acids were generally retained by the copepods it seems that fatty acids or even lipids were selectively accumulated and turned over due to bodily requirements, and thus, essential polyunsaturated fatty acids were preferentially retained. During feeding mixing, accumulation, and exchange of internal and dietary fatty acids and alcohols occurred as well as utilisation of lipids from both sources for metabolic requirements. The differences in lipid assimilation fit to the different life strategies of the copepods.     

Isolation and structural characterisation of two antibacterial free fatty acids from the marine diatom, <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis>

One solution to the global crisis of antibiotic resistance is the discovery of novel antimicrobial compounds for clinical application. Marine organisms are an attractive and, as yet, relatively untapped resource of new natural products. Cell extracts from the marine diatom, Phaeodactylum tricornutum, have antibacterial activity and the fatty acid, eicosapentaenoic acid (EPA), has been identified as one compound responsible for this activity. During the isolation of EPA, it became apparent that the extracts contained further antibacterial compounds. The present study was undertaken to isolate these additional antibacterial factors using silica column chromatography and reverse-phase high-performance liquid chromatography. Two antibacterial fractions, each containing a pure compound, were isolated and their chemical structures were investigated by mass spectrometry and nuclear magnetic resonance spectroscopy. The antibacterial compounds were identified as the monounsaturated fatty acid (9Z)-hexadecenoic acid (palmitoleic acid; C16:1 n-7) and the relatively unusual polyunsaturated fatty acid (6Z, 9Z, 12Z)-hexadecatrienoic acid (HTA; C16:3 n-4). Both are active against Gram-positive bacteria with HTA further inhibitory to the growth of the Gram-negative marine pathogen, Listonella anguillarum. Palmitoleic acid is active at micro-molar concentrations, kills bacteria rapidly, and is highly active against multidrug-resistant Staphylococcus aureus. These free fatty acids warrant further investigation as a new potential therapy for drug-resistant infections.     

Plastidial acyl carrier protein Δ9-desaturase modulates eicosapentaenoic acid biosynthesis and triacylglycerol accumulation in Phaeodactylum tricornutum

The unicellular marine diatom Phaeodactylum tricornutum accumulates up to 35% eicosapentaenoic acid (EPA, 20:5n3) and has been used as a model organism to study long chain polyunsaturated fatty acids (LC-PUFA) biosynthesis due to an excellent annotated genome sequence and established transformation system. In P. tricornutum, the majority of EPA accumulates in polar lipids, particularly in galactolipids such as mono- and di-galactosyldiacylglycerol. LC-PUFA biosynthesis is considered to start from oleic acid (18:1n9). EPA can be synthesized via a series of desaturation and elongation steps occurring at the endoplasmic reticulum and newly synthesized EPA is then imported into the plastids for incorporation into galactolipids via an unknown route. The basis for the flux of EPA is fundamental to understanding LC-PUFA biosynthesis in diatoms. We used P. tricornutum to study acyl modifying activities, upstream of 18:1n9, on subsequent LC-PUFA biosynthesis. We identified the gene coding for the plastidial acyl carrier protein Δ9-desaturase, a key enzyme in fatty acid modification and analyzed the impact of overexpression and knock out of this gene on glycerolipid metabolism. This revealed a previously unknown role of this soluble desaturase in EPA synthesis and production of triacylglycerol. This study provides further insight into the distinctive nature of lipid metabolism in the marine diatom P. tricornutum and suggests additional approaches for tailoring oil composition in microalgae.     

Effect of sex,dietary glycerol or dietary fat during late fattening,on fatty acid composition and positional distribution of fatty acids within the triglyceride in pigs

The effect of sex, source of saturated fat (lard v. palm oil) and glycerol inclusion in the fattening diet on composition and fatty acid positional distribution in the triglyceride molecule was studied in pigs from 78 to 110 kg BW. Average daily gain and carcass characteristics, including ham and loin weight, were not affected by dietary treatment but sex affected backfat depth (P<0.01). A significant interaction between sex and glycerol inclusion was observed; dietary glycerol increased lean content in gilts but not in barrows (P<0.05 for the interaction). Individual and total saturated fatty acid (SFA) concentrations were greater in barrows than in gilts. In contrast, the concentration of total polyunsaturated fatty acids (PUFA) and of C18:2n-6, C18:3n-3, C20:3n-9 and C20:4n-6 in the intramuscular fat (IMF) was higher (P<0.05) in gilts than in barrows. Sex did not affect total monounsaturated fatty acids (MUFA) concentration in the IMF. The proportion of SFA in the subcutaneous fat (SF) was higher in barrows than in gilts (P<0.001). Within the individual SFA, sex affected only the concentrations of C14:0 and C16:0 (P<0.001). Dietary fat did not affect total SFA or PUFA concentrations of the IMF but the subcutaneous total MUFA concentration tended to be higher (P=0.079) in pigs fed lard than in pigs fed palm oil. Dietary glycerol increased total MUFA and C18:1n-9 concentration in the IMF and increased total MUFA and decreased C18:2n-6, C18:3n-3 and total PUFA concentrations in the SF. The data indicate that altering the fatty acid composition of the triglyceride molecule at the 2-position, by dietary intervention during the fattening phase, is very limited.     

Fatty acids from 11 marine macroalgae of the French Brittany coast

Four species of red marine algae (Rhodophyceae), five species of brown marine algae (Pheophyceae) and two species of green marine algae (Chlorophyceae) were examined for the fatty acid composition of the three lipid groups separated by silica gel column chromatography (neutral lipids, glycolipids, phospholipids). The four red algae had high contents of 16:0 and C20-polyunsaturated fatty acids (PUFA), 20:5n-3 ranging from 18 to 49% of the total fatty acid content and 20:4n-6 from 1.4 to 22.5%, these fatty acids were evenly distributed in all lipid groups. The five brown algae had high contents of 18:1n-9, 18:2n-6 and 18:3n-3 but low content of 20:5n-3. No precise trend was detected for the distribution of these fatty acids in the three lipid groups. The two green algae had high contents of 16:0, 18:1n-7 and 18:3n-3 and a very low content of PUFA. They contained also large amounts of 16:4n-3 together with 16:2n-6 and 16:3n-3. While 16:2n-6 was mainly found in phospholipids, 16:4n-3 was mainly distributed in neutral lipids and glycolipids.Porphyra umbilicalis represents the richest source of 20:5n-3 whileUndaria pinnatifida can be selected when a balanced mixture of (n-6) and (n-3) PUFA is required.Author for correspondence     

Effects of Temperature and Dietary Lipids on Phospholipid Fatty Acids and Membrane Fluidity in Steinernema carpocapsae

The phospholipid composition of Steinernema carpocapsae was studied in relation to diet and culture temperature. When reared at 18 and 27.5 C on Galleria mellonella or on an artificial diet supplemented with lard, linseed oil, or fish oil as lipid sources, nematode phospholipids contained an abundance of 20-carbon polyunsaturated fatty acids, with eicosapentaenoic acid (20:5(n - 3)) predominant, regardless of the fatty acid composition of the diet. Because the level of linolenic acid (18:3(n - 3)) in nematode phospholipids was very low and because eicosapentaenoic acid was present even when its precursor (linolenic acid) was undetectable in the diet, S. carpocapsae likely produces n - 3 polyunsaturated fatty acids by de novo biosynthesis, a pathway seldom reported in eukaryotic animals. Reduction of growth temperature from 25 to 18 C increased the proportion of 20:5(n - 3) but not other polyunsaturated fatty acids. A fluorescence polarization technique revealed that vesicles produced from phospholipids of nematodes reared at 18 C were less ordered than those from nematodes reared at 27.5 C, especially in the outermost region of the bilayer. Dietary fish oil increased fluidity in the outermost region but increased rigidity in deeper regions. Therefore, S. carpocapsae appears to modify its membrane physical state in response to temperature, and eicosapentaenoic acid may be involved in this response. The results also indicate that nematode membrane physical state can be modified dietarily, possibly to the benefit of host-finding or survival of S. carpocapsae at low temperatures.     

Effect of varying levels of dietary essential fatty acid during early ontogeny of the sea scallop Placopecten magellanicus

This study investigated the biological effects of various dietary essential fatty acids levels to sea scallop larvae, Placopecten magellanicus. Scallop larvae were fed three diets from D-veliger to settlement. Diet A consisted of Isochrysis sp. and Pavlova lutheri, diet B was a mix of Isochrysis sp. and Chaetoceros muelleri and diet C consisted of the same two species, but C. muelleri was grown under silicate deprivation to alter the fatty acid composition. Pediveligers (28 days old) were sampled prior to settlement for fatty acid analysis, growth measurement and survival assessment. Survival and settlement success were measured at the end of the experiment (day 40). Our results show that feeding regime greatly influenced larval size, settlement and fatty acid composition. Diet A was severely deficient in arachidonic acid (20:4n-6, AA), leading to the poorest larval growth, survival and lipid content. Nevertheless, larvae fed diet A selectively accumulate AA by a factor three compared to the dietary amount. Shell size of 28-day-old larvae was positively correlated with AA content and negatively correlated with eicosapentaenoic acid (20:5n-3, EPA)-AA ratio, thus suggesting that these two variables are of major interest for the optimisation of larval growth in sea scallops. Finally, larvae fed diet C displayed 20% higher shell size at day 28 than larvae fed diet A and B, likely in relation to the dietary amount of saturated fatty acid (SFA). However, the moderate survival and settlement success of these groups of larvae might be associated with a relative deficiency in docosahexaenoic acid (22:6n-3, DHA). This study underlines that the overall balance between polyunsaturated fatty acid (PUFA) needs to be considered to adequately fed sea scallop larvae.     

Lipids in Arctic benthos: does the fatty acid and alcohol composition reflect feeding and trophic interactions?

Arctic benthic organisms of various taxa (Anthozoa, Polychaeta, Pantopoda, Crustacea, Echinodermata) were collected on the shelves off northeast Greenland, Spitsbergen and the western Barents Sea. Their fatty acid compositions were generally characterised by the predominance of the polyunsaturated fatty acids 20:5(n-3) and 22:6(n-3) together with the saturated fatty acid 16:0, which reflect the dominance of phospholipids. The fatty acid compositions of most benthic specimens were influenced by fatty acids of dietary origin. High amounts of the fatty acid 16:1(n-7), typical of diatoms, were found in different taxa from the northeast Greenland shelf. The 18:4(n-3) fatty acid, often typical of non-diatom input, was only dominant in Ophiopholis aculeata from the Spitsbergen shelf. In some taxa small amounts of wax esters were detected with alcohol moieties similar to those of the dominant Arctic copepods. The occurrence of intact wax esters, as well as the wax ester typical fatty acids 20:1(n-9) and 22:1(n-11), also suggested ingestion of large herbivorous copepods. An unusual fatty acid composition was found for most brittle stars, due to a ratio of the 18:1(n-9) and (n-7) fatty acid isomers below 1 with lowest ratios of 0.1. A similar low ratio was also detected in the polychaete Onuphis conchylega. The extremely low portions of the 18:1(n-9) fatty acid are striking, since carnivores are generally characterised by high levels of this fatty acid. A clear gradient from low 18:1(n-9) to (n-7) ratios in suspension feeders, via predatory decapods, to higher ratios in the scavenging amphipods was a major characteristic of the benthic species. Our investigations showed that lipid analyses can give important hints on trophic relationships of benthic species and may serve as means to establish the intensity of pelagic-benthic coupling.     

Lipid Content and fatty acid composition of algal communities in sea-ice and water from the Weddell Sea (Antarctica)

The lipid and fatty acid compositions of microalgae were investigated in sea-ice and water samples from six different habitats of the Weddell Sea (Antarctica). All sea-ice samples and ice-associated water contained high algal biomass dominated by centric and pennate diatoms. Cells partially filled with oil droplets and resting spores were found. In the cells from the ice platelet layer triacylglycerols formed the largest component of the lipids. The fatty acid composition of sea-ice microalgae was dominated by the 16:1(n-7), 16:0, 18:1(n-9) and 20:5 (n-3) fatty acids. Except 18:1, they are typical for diatom fatty acids. These fatty acids were most abundant in pieces of first year ice with a brown colouration (brown-ice) and in the water column directly below sea-ice (sub-ice water). The small amounts of non-diatom acids, as 22:6 (n-3) and 18:4 (n-3), clearly showed that the sea-ice communities were not purely composed of diatoms. The most striking difference, in comparison to the general fatty acid composition of diatoms, was the high proportion of the 18:1 fatty acid in all samples, which might be caused by detrital material or lipid accumulation within cells and resting spores. In general, no clear adaptation of the fatty acid composition to the Antarctic and sea-ice environment was found. The fatty acid composition of the particulate matter from the water column was totally different from all other samples dominated by the saturated fatty acids 16:0 and 18:0.     

Alterations of the fatty acid composition and lipid metabolome of breast muscle in chickens exposed to dietary mixed edible oils

The fatty acid composition of chicken’s meat is largely influenced by dietary lipids, which are often used as supplements to increase dietary caloric density. The underlying key metabolites and pathways influenced by dietary oils remain poorly known in chickens. The objective of this study was to explore the underlying metabolic mechanisms of how diets supplemented with mixed or a single oil with distinct fatty acid composition influence the fatty acid profile in breast muscle of Qingyuan chickens. Birds were fed a corn-soybean meal diet supplemented with either soybean oil (control, CON) or equal amounts of mixed edible oils (MEO; soybean oil : lard : fish oil : coconut oil = 1 : 1 : 0.5 : 0.5) from 1 to 120 days of age. Growth performance and fatty acid composition of muscle lipids were analysed. LC-MS was applied to investigate the effects of CON v. MEO diets on lipid-related metabolites in the muscle of chickens at day 120. Compared with the CON diet, chickens fed the MEO diet had a lower feed conversion ratio (P < 0.05), higher proportions of lauric acid (C12:0), myristic acid (C14:0), palmitoleic acid (C16:1n-7), oleic acid (C18:1n-9), EPA (C20:5n-3) and DHA (C22:6n-3), and a lower linoleic acid (C18:2n-6) content in breast muscle (P < 0.05). Muscle metabolome profiling showed that the most differentially abundant metabolites are phospholipids, including phosphatidylcholines (PC) and phosphatidylethanolamines (PE), which enriched the glycerophospholipid metabolism (P < 0.05). These key differentially abundant metabolites – PC (14:0/20:4), PC (18:1/14:1), PC (18:0/14:1), PC (18:0/18:4), PC (20:0/18:4), PE (22:0/P-16:0), PE (24:0/20:5), PE (22:2/P-18:1), PE (24:0/18:4) – were closely associated with the contents of C12:0, C14:0, DHA and C18:2n-6 in muscle lipids (P < 0.05). The content of glutathione metabolite was higher with MEO than CON diet (P < 0.05). Based on these results, it can be concluded that the diet supplemented with MEO reduced the feed conversion ratio, enriched the content of n-3 fatty acids and modified the related metabolites (including PC, PE and glutathione) in breast muscle of chickens.     

Effect of selection for intramuscular fat on the fatty acid composition of rabbit meat

Intramuscular fat (IMF) content and composition are relevant for the meat industry due to their effect on human health and meat organoleptic properties. A divergent selection experiment for IMF of Longissimus dorsi (LD) muscle was performed in rabbits during eight generations. The aim of this study is to estimate the correlated responses to selection for IMF on the fatty acid composition of LD. Response to selection for IMF was 0.34 g/100 g of LD, representing 2.4 phenotypic SD of the trait. High-IMF line showed 9.20% more monounsaturated fatty acids (MUFA) and 0.39%, 9.97% and 10.3% less n-3, n-6 and polyunsaturated fatty acids (PUFA), respectively, than low-IMF line. The main MUFA and PUFA individual fatty acids followed a similar pattern, except for C18:3n-3 that was greater in the high-IMF line. We did not observe differences between lines for the percentage of total saturated fatty acids, although high-IMF line showed greater C14:0 and C16:0 and lower C18:0 percentages than low-IMF line. Heritability estimates were generally high for all fatty acids percentages, ranging from 0.43 to 0.59 with a SD around 0.08, showing an important genetic component on these traits. Genetic correlations between IMF and LD fatty acid percentages were strong and positive for C14:0, C16:1, C18:1n-9, and MUFA, ranging from 0.88 to 0.97, and strong and negative for C18:0, C18:2n-6, C20:4n-6, n-6 and PUFA, ranging from −0.83 to −0.91. These correlations were accurately estimated, with SD ranging from 0.02 to 0.06. The genetic correlations between IMF and other fatty acids were estimated with lower accuracy. In general, phenotypic and genetic correlations were of the same order. Our experiment shows that selection for IMF strongly affects the fatty acid composition of meat, due the high heritabilities of fatty acids and their high genetic correlations with IMF.     

The effect of low temperature on fatty acid composition and tocopherols of the red microalga, <Emphasis Type="Italic">Porphyridium cruentum</Emphasis>

Porphyridium cruentum was grown in 10 L batch culture at 18°C, pH 8.0 and 28‰ salinity. The cells were harvested in the stationary phase and the fatty acid composition analysed by GC and tocopherol content by HPLC. A total of 14 fatty acids were identified including saturated fatty acids (13:0, 14:0, 14:0 iso, 15:0, 16:0, 16:0iso) and monounsaturated fatty acids (MUFAs; 16:1(n-7), 18:1(n-7), 18:1(n-9). Polyunsaturated fatty acids (PUFAs) were the predominant fatty acids detected, reaching 43.7% of total fatty acids in the stationary phase of culture. Among the PUFAs, eicosapentaenoic acid (EPA, 20:5(n-3)) was dominant (25.4%), followed by 12.8% arachidonic acid (AA, 20:4(n-6)). α-Tocopherol and γ-tocopherol contents were 55.2 μg g⁻¹ dry weight and 51.3 μg g⁻¹ dry weight respectively.     

Gram-scale purification of eicosapentaenoic acid (EPA, 20:5n-3) from wetPhaeodactylum tricornutum UTEX 640 biomass

Eicosapentaenoic acid (EPA, 20:5n-3) was obtained from the microalgaPhaeodactylum tricornutum following a three-step process: fatty acid extraction by direct saponification of wet biomass, polyunsaturated fatty acid (PUFA) concentration by formation of urea inclusion compounds and EPA isolation by preparative HPLC. Direct saponification of wet biomass was carried out with KOH-ethanol (96% v:v) (1 h, 60 °C), extracting 91% of the EPA. PUFAs were concentrated by the urea method with an urea/fatty acid ratio of 4:1 at a crystallization temperature of 28 °C using methanol as the urea solvent. An EPA concentration ratio of 1.5 (55.2/36.3) and recovery of 79% were obtained. This PUFA concentrate was used to obtain 95.8% pure EPA by preparative HPLC, using a reverse-phase column (C₁₈, 4.7 cm i.d. × 30 cm) and methanol-water (1% AcH) 80:20 w/w as the mobile phase. Ninety-seven per cent of EPA loaded was recovered and 70% EPA present in theP. tricornutum biomass was recovered in a highly pure form by means of this three-step downstream processing. In each of the HPLC preparative runs, 635 mg PUFA concentrate were loaded, obtaining 326 mg of a highly concentrated EPA fraction (2.46 g d^–1). Finally, a preliminary cost statement has been calculated.